Electric compressed-gas circuit breaker

ABSTRACT

In order to avoid flow stagnation near the sliding contact ring of arc-resistant material, auxiliary flow passages are provided to pass at least a portion of the quenching gas flow across the contact ring during a breaker opening motion. The auxiliary flow passages can be formed to bypass a gas flow between the sliding bridging switching element and the downstream contact, e.g. through holes in the contact downstream of the nozzle or through passages in the nozzle. The auxiliary flow passages can also take the form of radial holes through the bridging switching element and contact ring itself.

United States Patent 9 Goedecke et al.

[451 Dec. 17,1974

[ ELECTRIC COMPRESSED-GAS CIRCUIT BREAKER [75] Inventors: HeikoGoedecke; Klaus-Peter Rolff;

Friedrich Richter, all of Berlin, Germany [73] Assignee: SiemensAktiengesellschaft, Munich,

Germany [22] Filed: Mar 22, 1973 [21] Appl. No.: 344,043

[30] Foreign Application Priority Data 7 Mar. 27, 1972 Germany 2215656[52] US. Cl 200/148 R [51] lntLCl. HOlh 33/82 [58] Field of Search200/148 R, 148 B, 148 BV, 200/148 A, 150 G [56] References Cited FOREIGNPATENTS OR APPLICATIONS Germany 200/148 R Primary Examiner-Robert S.Macon Attorney, Agent, or FirmKenyon & Kenyon Reilly Carr & Chapin [57]ABSTRACT ln order to avoid flow stagnation near the sliding contact ringof arc-resistant material, auxiliary flow passages are provided to passat least a portion of the quenching gas flow across the contact ringduring a breaker opening motion.

The auxiliary flow passages can be formed to bypass a gas flow betweenthe sliding bridging switching element and the downstream contact, e.gthrough holes in the contact downstream of the nozzle or throughpassages in the nozzle. -The auxiliary flow passages can also take theform of radial holes through the bridging switching element and contactring itself.

22 Claims, 7 Drawing Figures ELECTRIC COMPRESSED-GAS CIRCUIT BREAKERFIELD OF THE INVENTION The invention relates to an electriccompressed-gas circuit breaker.

BACKGROUND OF THE INVENTION I-Ieretofore, various types of electriccompressed-gas circuit breakers have been known. For example, one typehas been constructed witha blasting device consisting of a piston andcylinder, with two stationary nozzle-shaped contacts, and with abridging switching element surrounding these contacts and connecting thecontacts in a closed breaker position. This circuit breaker is usuallyequipped with a sliding contact ring constructed of arc-resistantmaterial and spring loaded contact fingers ln order to improve the arccommutation during a breaker opening process, it has been proposed inpending US. patent application Ser. No. 334,934, filed'Feb. 22, 1973.and entitled Electric Compressed-Gas Circuit Breaker, corresponding toGerman patent application P 22 09 287.1, filed Feb. 22, 1972 to have thebridging switching element carry the sliding contact ring with anelectrically insulating layer interposed therebetween and to have thesliding contact ring and the contactfingerselectrically connected at thetime .of separation of the contact fingers from'the one stationarycontact.

However, in high-power breakers, due to the required largecross-section, the bridging switching element, which surrounds one ofthe stationary contacts even during thebreaker-opening motion canrequire a construction of the contact arrangement which causes the gapbetween the'two contacts to be at least partially the breaker-openingmotion permits avoidance of flow separation areas in the quenching gasflow. By application of the invention, a path of flow is produced in thegap between the two stationary contacts, which has favorable quenchingand cooling properties, and therefore accomplishes an increase in thecircuit-breaking capabilities.

In a first embodiment of the compressed circuit breaker, according tothe invention, the auxiliary passage means is in the form of at leastone passage which begins in the region of the gap between the twostationary'contacts and terminates behind a nozzle located in the end ofone of the contacts. Here, the auxiliary passage can run between theouter surface of one nozzlecontaining contact and the bridging switchingelement surrounding the contact. In this case, the outlet of theauxiliary passage is formed of at least one radially oriobstructedduring breaker opening. This can cause hot quenching gas to collect inaregion of flow stagnation in frontof the sliding contact ring.

' OBJECT OF THE INVENTION I It is an object of the invention toeliminate the region of flow stagnation'in' electric compressed-gascircuit breakers in'order to achieve improved circuit-breakingcapability. I l t SUMMARY OF THE INVENTION The invention provides anelectric compressed-gas circuit breaker having two hollow contactsdisposed in spaced relation, means including a bridging switchingeIement-slidably surrounding the contacts for selectively electricallyconnecting the contacts in a closed breaker condition, a contact ring ofarc-resistant material mounted on the bridging switching element, andmeans defining a chamber about the bridging switching element for apressurized quenching gas with an auxiliary passage means for passing atleast a portion of the quenching gas from the gas chamber across thecontact ring during a breaker opening operation.

The auxiliary passage means is closed in the closed breaker position andis automatically opened during the breaker-opening motion. The auxiliarypassage means is disposed in the usual gas flow channel between themeans which defines the quenching gas chamber and the hollow contacts.

The component of quenching gas flow fed to the sliding contact ring bythe auxiliary passage means during ented continuous hole in the hollowcontact, located behind the nozzle in the direction of flow.Alternatively, insofar as there isa decrease in contact crosssectionwhere cavities are placed in the contact which is undesirable forelectrical reasons, the cavities can be placed in the nozzles forexample by milling cuts running parallel to the nozzleaxis.

In both cases, several passages or cavities can advantageously bedistributed around the circumference. In the embodiment with holes inthe hollow contact, the nozzle connected with the contact becomes asimple structure of circular symmetry, which permits the use of, forexample, graphite as the arc-resistant material.

Also, in both embodiments, the flow of quenching gas is branched in theoutflow directionb ehind' the sliding contact ring; the main flow branchflowing through the interior of the nozzle of the one stationary contactwhile the other branch flows through the auxiliary passage. Thedimensions ofthe branches can be made so that the flow of quenchinggasdriving the are into the center of the gap between the stationarycontacts is decreased only slightly or not at all.

In a further embodiment, the auxiliary passage means I is formed bydrilling at least one hole transversely to the axis of the bridgingswitching elementQand passing through the switching element, aninsulating layer between the switching element and the contact ring andthe sliding contact ring itself. Here, too, several drill holes can bedistributed over the circumference. In this embodiment, the quenchinggasflow is branched in the outflow direction before the sliding contactring is reunited behind the sliding contact ring, which is advantageousin some cases.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates afragmentary crosssectional view of an electric compressed-gas circuitFIG. 5 illustrates a view similar to FIG. 3 of a modified circuitbreaker in accordance with the invention;

FIG. 6 illustrates a view taken on line 6-6 of FIG.

and

FIG. 7 illustrates a view similar to FIG. 3 of a further modifiedcircuit breaker according to the invention.

' PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. .1, thepressurized-gas circuit breaker, such as for a high voltage linecarrying, for example, 110 kilovolts (KV), uses sulfur hexafluoride as aquenching and insulatingmedium. For the sake of simplicity, only thoseparts of the circuit breaker necessary for an understanding of theinvention are shown.

. are connected in a closed breaker position by a tubular bridgingswitching element 6. The bridging switching element'6 has a pluralityofspring-loaded contact fingers 7 mounted on the inside. Each finger 7 hasa contact surface 8 at each opposite end which exerts a predeterminedcontact pressure against the respective stationary contact 3, 4. Thebridging switching element 6 also carries asliding contact ring 9consisting of areresistant, electrically conductive material, with aninterposed electrically insulating layer 10. Thebridging switchingelement 6 is screwed into a coupling structure 18, connected by mountinghardware 19 to an insulating tube 20 which forms a blast cylinder. Theupper edge 21 of the blast cylinder 20 carries a nozzle which slidablysurrounds the stationary contact 3. The blast cylinder 20 isco'nstructedin one piece,"e .g. of fiber-reinforced plastic.

In addition, the coupling structure 18 is connected to a plurality oftension rods 12, each of which is pivotally secured to the couplingstructure by a pin 13 integral with the coupling structure 18. A drivemember (not shown) is coupled to the tension rods 12 and moves thecircuit breaker from a closed breaker position, shown on the right asviewed, to an open breaker position, shown'on the left. as is known. Astationary piston 24 is also mounted, as is known, in sealed slidablerelation between the bridging switching element6 and the blast cylinder20.

The switching chamber is totally filled with a quenching. gas, such assulfur hexaflouride, at a pressure of, e.g. 4 atmospheres.

When the breaker opens, the bridging switching element 6 together withthe blast cylinder 20 moves against the fixed piston 24 in the downwarddirection. This causes the sulfur hexafluoride present within the blastcylinder 20 to be compressed, since the gas cannot flow out at thebeginning of the breaker-opening motion. Only when the blast cylinder 20has completed approximately one-half of a stroke do the contact fingers7 of the bridging switching element 6 and the sliding contact ring 9slide off the stationary contact 3. As a result, an electricalseparation occurs between the contacts 3, 4 as well as the formation ofa clearance, or gap, for gas outflow. The previouslycompressed sulfurhexafluoride then flows through this gap into the outflow nozzles 3a, 4amounted on the stationary contacts 3, 4. This causes the arc to becommutated from the sliding contact ring 9 over the outflow nozzle 4a onthe stationary contact 4, and then quenched.

In the open breaker condition, the electric field in- .tensity in thegap is kept as small as possible by appropriate design of thelarge-surfaced nozzles 3a, 4b which act as electrodes.

Referring to FIG. 2, for high required breaker power with acorrespondingly strong flow of quenching gas and comparatively highcross-sections of the sliding contact ring 9, a flow stagnation,asshown, can form in the quenching gas flow between the bridgingswitching element 6 and the nozzle 4aof the stationary contact 4. Thus,under certain circumstances the arc is not sufficiently blasted in theregion of the sliding contact ring 9, and the heated and ionizedquenching gas present there flows out only after a delay.

Referring to FIGS. 3 and 4, wherein like reference characters indicatelike parts as above, in order to avoid any flow stagnation, an auxiliarypassage means in the form of a passage or bypass 40 is added to theflow'channel between the bridging switch element 6 and the hollowcontacts 3, ,4 to feed quenching gas to the sliding contact ring 9. Thispassage or bypass 40 is closed to the flow of quenching gas in theclosed breaker condition of the bridging switching element 6, and isautomatically opened during the breakeropening motion. The passage 40terminates in a plurality of radially disposed holes 42 in the contact 4behind the nozzle 4a. When a breaker-openingmotion occurs, a quenchinggas flow 41 is branched in the direction of flow behind the slidingcontact ring 9, so that one flow portion 41a flows through the interiorof the nozzle 4a, while another flow portion 41b flows through theauxiliary passage. 40 to the holes 42 and then into the nozzle 4a. P

'Referring to FIGS. Sjand 6, wherein like reference characters indicatelike parts as abov9, the auxiliary passage means can also be formed bycavities in the nozzle 4a of the stationary contact 4 so that quenchinggas is fed to the sliding contact ring 9. Here, too, the auxiliarypassage means 50 is closed in the closed breaker condition of thebridging switching element 6, and is automatically opened during thebreakeropening motion.v

As may be seen in FIGS. 4 and 6, several passage means 40, 50respectively are distributed overthe cir-.

cumference of the nozzle 4 in order to achieve a quenching gas flow thatis evenly distributed over the circumference of the sliding contact ring9.

Referring to FIG. 7, wherein like reference characters indicate likeparts as above, an auxiliary passage means is formed by at least onedrill hole disposed transversely to the axis of the bridging switchingelement 6 and passing through the element 6, the insulating layer 10 andthe sliding contact ring 9. This auxiliary hole 60 is closed until thesliding contact ring 9 is lifted off from the nozzle 3a of thestationary contact 3, and is automatically opened as the breaker-openingmotion of the bridging switching element 6 proceeds.

Several drill holes 60 are advantageously distributed over thecircumference of the element 6 to obtain a quenching-gas flow that isevenly distributed over the circumference of the sliding contact ring 9.

In use, the drill holes 60 form nozzles directed toward the axis of thecontacts 3, 4, which feed additional quenching gas into the gap betweenthe contacts 3, 4 during thebreaker-opening motion. The drill holes 60are arranged to feed the quenching gas into the gap in an essentiallyradial direction. As shown, the outlets of the nozzles 60 are located inthat part of the electrode surface that is near theend face of thebridging switching element 6 It is possible within the scope of theinvention, to add a guiding structure on the sliding contact ring 9which acts as the arc electrode so that the guiding structure is at, orconstitutes, the free upper edge of the bridging switching element 6 andcan accommodate some of the nozzles 60 such that these would terminatein the guiding structure. The dimensions of the effective cross sectionof all nozzles are then advantageously made so that the quenching gasflow through the nozzles comprises only asmall part of the total flow ofquenching gas through the outflow cross-section of the end face of thebridging switching element 6."At least some of these nozzles 60 wouldend at the surface of the sliding contact ring 9 that carries the arc.-

What is claimed is: t 1. ln an electric compressed-gas circuit breaker,a contact arrangement comprising: two stationary-mutuallyadjacentcontact pieces; a bridging switching unit movable between closedand open positions forelectriplurality of elongated contact elementsdisposed in said supporting body for electrically connecting saidcontact pieces when said switching unit is in the closed position, andspring means for spring loading said contact elements to displace thesame into electrically conductive contact with said slide contact ringas said ring and said contact elements separate from said other contactpiece when said switching unit moves into the open position. i

3. In an electric compressed-gas circuit breaker as set forth in claim 1wherein said one contact piece has a of said one contact piece and saidbridging switching unit.

5. The contact arrangement of claim 4, at least one radially directedbore formed in said one contact piece behind said nozzle, said borecommunicating with said space and constitutingthe outlet of said passageto the hollow interior of said one contact piece.

from said region to'the interior of the hollow contact cally bridgingsaid contact pieces in the closed position i and for electricallydisconnecting said contact pieces in the open position whereby an arcdevelops when said switching unitis moved to the open positiomsaidswitching unit being mountedon one of said contact pieces so as todefine a'gap'betwe en said switching unit and the'other one'of said'contact pieces when said switching unit is moved to said open position;a slide contact ring of arc-resistant material mounted on said bridgingswitching unit for slideably engaging said other contact piece in theclosed position andfo'r being in spaced relation to'said contact pieceacross said gap when said switching unit is moved to the open position;compressed-gas chamber" means for blasting compressed-gas through saidgap when said switching unit separates from said other contact pieceduring the movement thereof to said open position; at least said onecontact piece being hollow to define a flow path for conducting the gasaway from the gap; said one contact piece and said switching unitconjointly defining, during the movement of said switching unit to saidopen position, a region at least partially shielded from the flow ofthegasthrough said gap; and, auxiliary passage means communicating withsaid region for causing at least a portion of the compressed-gas to flowthrough said region when said switching unitseparates from said othercontact piece during the movement thereof to said open position wherebyflow stagnation of gas in said region is prevented.

2. The contact arrangement of claim 1, said switching unit including asupporting body, electrical insulation disposed at said supporting body,said contact ring being mounted on said electrical insulation, saidinsulation being disposed between said supporting body and said ringthereby insulating said ring from said body, a

piece. i 7. The contact arrangement of claim 1 wherein said one contactpiece has a nozzle in the end thereoffacing said other contact piece,said auxiliary passage means being a plurality of cavitiesdistributedabout the periphery of said nozzle, each one of said cavities extendingfrom said region to the interior of said one contact piece.

passage means comprising at least one bore passing through said ring andsaid insulation and extending transverse to the longitudinal axis ofsaid switching unit so as to communicate at one end thereof with saidchamber means, said contact ring and said other contact piece conjointlydefining an interface when said switching unit is in said closedposition, said bore having an outlet at said interface whereby said boreis closed off in said closed position and during the opening movement ofsaid switching unit until said contact ring separates from said othercontact piece whereafter said bore is opened to communicate also withsaid gap and with said partially shielded region.

9. The contact arrangement of claim 2, saidauxiliary H passage meanscomprising a plurality of bores disposed about the periphery of saidslide contact ring, each ofv 8. The contact arrangement of claim 2, saidauxiliary to communicate also with said gap and with said partiallyshielded region.

10. The contact arrangement of claim 1, said auxiliary passage meanscomprising at least one bore passing through said ring and extendingtransverse to the longitudinal axis of said switching unit so as tocommunicate at one end thereof with said chamber means, said contactring and said other contact piece conjointly defining an interface whensaid switching unit is in said closed position, said bore having anoutlet at said interface whereby said bore is closed off in said closedposition and during the opening movement of said switching unit untilsaid contact ring separates from said other contact piece whereaftersaid bore is opened to communicate also with said gap and with saidpartially shielded region.

11. The contact arrangement of claim .1, said auxiliary passage meanscomprising a plurality of bores disposed about the periphery of saidslide contact ring, each of said bores passing through said ring andextending transverse to the longitudinal axis of said switching unit soas to communicate at one end thereof with said chamber means, saidcontact ring and said other contact piece conjointly defining aninterface when said'switching unit is in said closed position, each ofsaid bores having an outlet at said interface whereby each'of said boresis closed off in said closed position and during the'openingmovement ofsaidswitching unit until said contact ring separates from said othercontact piece whereafter each of said bores is opened to communicatealso with said gap and with said partially shielded region.

12. in an electric compressed-gas circuit breaker as set forth. in claimI wherein said auxiliary passage means includes a plurality of passagesdistributed over the circumference of'said one contact.

13. in an electric compressed-gas circuit breaker having two hollowstationary contacts disposed in spaced relation, means including abridging switching element slidably surrounding said contacts forselectively electrically connecting said contacts in a closed breakerposition and being mounted on one of said contacts in an open breakerposition in spaced relation to the other of said contacts, a contactring of arcresistant material mounted on said bridging switching elementto be disposed in spaced relation to said other of said contacts acrossa gap when said bridging switching element is moved during a breakeropening motion,

means defining a chamber about said bridging switching element for a'pressurized quenching gas to be flowed through said gap into saidcontact; and auxiliarypassage means for passing'at least a portion ofthe quenching gas from said chamber across said contact ring during saidbreaker opening motion, said auxiliary passage means being between theouter surface of said one contact and said bridging switching elementand being formed by at least one continuous radially oriented hole insaid one contact behind said nozzle.

14. in an electric compressed-gas circuit breaker having two hollowstationary contacts disposed in spaced relation, means including abridging switching element slidably surrounding said contacts forselectively electrically connecting said contacts in a closed breakerposition and being mounted on one of said contacts in an open breakerposition in spaced relation to the other of said contacts, a contactring of areresistant material mounted on said bridging switching elementto be disposed in spaced relation to said other of said contacts acrossa gap when said bridging switching element is moved during a breakeropening motion, means defining a chamber about said bridging switchingelement for a pressurized quenching gas to be flowed through said gapinto said contact; and auxiliary passage means for passing at least aportion of the quenching gas from said chamber across said contact ringduring said breaker opening motion, said auxiliary passage means beingbetween the outer surface of said one contact and said bridgingswitching element and being formed by at least one cavity in said nozzlerunning parallel to the contact axis of said contact.

15. In an electric compressed-gas circuit breaker having two hollowstationary contacts disposed in spaced relation, means including abridging switching element slidably surrounding said contacts forselectively electrically connecting said contacts in a closed breakerposition and being mounted on one of said contacts in an open breakerposition in spaced relation to theother of said contacts, a contact ringof arcresistant material mounted on said bridging switching element tobe disposed in spaced relation to said other of said contacts across agap when said bridging switching element is moved during a breakeropening motion, means defining a chamber about said bridging switchingelement for a pressurized quenching gas to be flowed through said gapinto said contact; and auxiliary passage means for. passing at least aportion of the quenching gas from said chamber across said contact ringduring said breaker opening motion, said auxiliary passage meansincluding at least one hole disposed transversely to the axisof saidbridging switching element and passing through said element and saidcontact ring.

16. In an electric compressed-gas circuit breaker as set forth in claim8, a plurality of said holes distributed over the circumference of saidcontact ring.

17. In an electric compressed-gas circuit breaker as 7 set forth inclaim 9 wherein said holes are in the form of nozzles.

18. In an electriccompressed-gas circuit breaker as set forth-in claim10 wherein at least some of said nozzles terminate in the surface ofsaid contact ring.

19. In an electric compressed-gas circuit breaker as set forth in claim10 wherein at least some of said nozzles terminate near the end face ofsaid bridging switching element. v

20. in an electric compressed-gas circuit breaker as set forth in claim8 wherein the effective cross section of said nozzles is controlled bythe motion of said bridg-' ing switching element. a

21. In an electric compressed-gas circuit breaker as set forth in claim8 wherein said nozzles are radially disposed tosaid contact ring.

22. In an electric compressed-gas circuit breaker as set forth in claim8 further including a guiding structure on said contact ring at the freeend face of said bridging switching element and at least some of saidholes terminate therein.

1. In an electric compressed-gas circuit breaker, a contact arrangementcomprising: two stationary mutually adjacent contact pieces; a bridgingswitching unit movable between closed and open positions forelectrically bridging said contact pieces in the closed position and forelectrically disconnecting said contact pieces in the open positionwhereby an arc develops when said switching unit is moved to the openposition, said switching unit being mounted on one of said contactpieces so as to define a gap between said switching unit and the otherone of said contact pieces when said switching unit is moved to saidopen position; a slide contact ring of arc-resistant material mounted onsaid bridging switching unit for slideably engaging said other contactpiece in the closed position and for being in spaced relation to saidcontact piece across said gap when said switching unit is moved to theopen position; compressed-gas chamber means for blasting compressed-gasthrough said gap when said switching unit separates from said othercontact piece during the movement thereof to said open position; atleast said one contact piece being hollow to define a flow path forconducting the gas away from the gap; said one contact piece and saidswitching unit conjointly defining, during the movement of saidswitching unit to said open position, a region at least partiallyshielded from the flow of the gas through said gap; and, auxiliarypassage means communicating with said region for causing at least aportion of the compressed-gas to flow through said region when saidswitching unit separates from said other contact piece during themovement thereof to said open position whereby flow stagnation of gas insaid region is prevented.
 2. The contact arrangement of claim 1, saidswitching unit including a supporting body, electrical insulationdisposed at said supporting body, said contact ring being mounted onsaid electrical insulation, said insulation being disposed between saidsupporting body and said ring thereby insulating said ring from saidbody, a plurality of elongated contact elements disposed in saidsupporting body for electrically connecting said contact pieces whensaid switching unit is in the closed position, and spring means forspring loading said contact elements to displace the same intoelectrically conductive contact with said slide contact ring as saidring and said contact elements separate from said other contact piecewhen said switching unit moves into the open position.
 3. In an electriccompressed-gas circuit breaker as set forth in claim 1 wherein said onecontact piece has a nozzle in the end thereof facing said other contactpiece for the flow of the quenching gas therethrough, said auxiliarypassage means including at least one passage extending from said regionand terminating behind said nozzle.
 4. In an electric compressed-gascircuit breaker as set forth in claim 3 wherein said auxiliary passagemeans includes a space conjointly defined by the outer surface of saidone contact piece and said bridging switching unit.
 5. The contactarrangement of claim 4, at least one radially directed bore formed insaid one contact piece behind said nozzle, said bore communicating withsaid space and constituting the outlet of said passage to the hollowinterior of said one contact piece.
 6. The contact arrangement of claim1 wherein said one contact piece has a nozzle in the end thereof facingsaid other contact piece, said auxiliary passage means being a cavityformed in said nozzle so as to extend from said region to the interiorof the hollow contact piece.
 7. The contact arrangement of claim 1wherein said one contact piece has a nozzle in the end thereof facingsaid other contact piece, said auxiliary passage means being a pluralityof cavities distributed about the periphery of said nozzle, each one ofsaid cavities extending from said region to the interior of said onecontact piece.
 8. The contact arrangement of claim 2, said auxiliarypassage means comprising at least one bore passing through said ring andsaid insulation and extending transverse to the longitudinal axis ofsaid switching unit so as to communicate at one end thereof with saidchamber means, said contact ring and said other contact piece conjointlydefining an interface when said switching unit is in said closedposition, said bore having an outlet at said iNterface whereby said boreis closed off in said closed position and during the opening movement ofsaid switching unit until said contact ring separates from said othercontact piece whereafter said bore is opened to communicate also withsaid gap and with said partially shielded region.
 9. The contactarrangement of claim 2, said auxiliary passage means comprising aplurality of bores disposed about the periphery of said slide contactring, each of said bores passing through said ring and said insulationand extending transverse to the longitudinal axis of said switching unitso as to communicate at one end thereof with said chamber means, saidcontact ring and said other contact piece conjointly defining aninterface when said switching unit is in said closed position, each ofsaid bores having an outlet at said interface whereby each of said boresis closed off in said closed position and during the opening movement ofsaid switching unit until said contact ring separates from said othercontact piece whereafter each of said bores is opened to communicatealso with said gap and with said partially shielded region.
 10. Thecontact arrangement of claim 1, said auxiliary passage means comprisingat least one bore passing through said ring and extending transverse tothe longitudinal axis of said switching unit so as to communicate at oneend thereof with said chamber means, said contact ring and said othercontact piece conjointly defining an interface when said switching unitis in said closed position, said bore having an outlet at said interfacewhereby said bore is closed off in said closed position and during theopening movement of said switching unit until said contact ringseparates from said other contact piece whereafter said bore is openedto communicate also with said gap and with said partially shieldedregion.
 11. The contact arrangement of claim 1, said auxiliary passagemeans comprising a plurality of bores disposed about the periphery ofsaid slide contact ring, each of said bores passing through said ringand extending transverse to the longitudinal axis of said switching unitso as to communicate at one end thereof with said chamber means, saidcontact ring and said other contact piece conjointly defining aninterface when said switching unit is in said closed position, each ofsaid bores having an outlet at said interface whereby each of said boresis closed off in said closed position and during the opening movement ofsaid switching unit until said contact ring separates from said othercontact piece whereafter each of said bores is opened to communicatealso with said gap and with said partially shielded region.
 12. In anelectric compressed-gas circuit breaker as set forth in claim 1 whereinsaid auxiliary passage means includes a plurality of passagesdistributed over the circumference of said one contact.
 13. In anelectric compressed-gas circuit breaker having two hollow stationarycontacts disposed in spaced relation, means including a bridgingswitching element slidably surrounding said contacts for selectivelyelectrically connecting said contacts in a closed breaker position andbeing mounted on one of said contacts in an open breaker position inspaced relation to the other of said contacts, a contact ring ofarc-resistant material mounted on said bridging switching element to bedisposed in spaced relation to said other of said contacts across a gapwhen said bridging switching element is moved during a breaker openingmotion, means defining a chamber about said bridging switching elementfor a pressurized quenching gas to be flowed through said gap into saidcontact; and auxiliary passage means for passing at least a portion ofthe quenching gas from said chamber across said contact ring during saidbreaker opening motion, said auxiliary passage means being between theouter surface of said one contact and said bridging switching elementand being formed by at least one continuous radially oriented hole insaid one conTact behind said nozzle.
 14. In an electric compressed-gascircuit breaker having two hollow stationary contacts disposed in spacedrelation, means including a bridging switching element slidablysurrounding said contacts for selectively electrically connecting saidcontacts in a closed breaker position and being mounted on one of saidcontacts in an open breaker position in spaced relation to the other ofsaid contacts, a contact ring of arc-resistant material mounted on saidbridging switching element to be disposed in spaced relation to saidother of said contacts across a gap when said bridging switching elementis moved during a breaker opening motion, means defining a chamber aboutsaid bridging switching element for a pressurized quenching gas to beflowed through said gap into said contact; and auxiliary passage meansfor passing at least a portion of the quenching gas from said chamberacross said contact ring during said breaker opening motion, saidauxiliary passage means being between the outer surface of said onecontact and said bridging switching element and being formed by at leastone cavity in said nozzle running parallel to the contact axis of saidcontact.
 15. In an electric compressed-gas circuit breaker having twohollow stationary contacts disposed in spaced relation, means includinga bridging switching element slidably surrounding said contacts forselectively electrically connecting said contacts in a closed breakerposition and being mounted on one of said contacts in an open breakerposition in spaced relation to the other of said contacts, a contactring of arc-resistant material mounted on said bridging switchingelement to be disposed in spaced relation to said other of said contactsacross a gap when said bridging switching element is moved during abreaker opening motion, means defining a chamber about said bridgingswitching element for a pressurized quenching gas to be flowed throughsaid gap into said contact; and auxiliary passage means for passing atleast a portion of the quenching gas from said chamber across saidcontact ring during said breaker opening motion, said auxiliary passagemeans including at least one hole disposed transversely to the axis ofsaid bridging switching element and passing through said element andsaid contact ring.
 16. In an electric compressed-gas circuit breaker asset forth in claim 8, a plurality of said holes distributed over thecircumference of said contact ring.
 17. In an electric compressed-gascircuit breaker as set forth in claim 9 wherein said holes are in theform of nozzles.
 18. In an electric compressed-gas circuit breaker asset forth in claim 10 wherein at least some of said nozzles terminate inthe surface of said contact ring.
 19. In an electric compressed-gascircuit breaker as set forth in claim 10 wherein at least some of saidnozzles terminate near the end face of said bridging switching element.20. In an electric compressed-gas circuit breaker as set forth in claim8 wherein the effective cross section of said nozzles is controlled bythe motion of said bridging switching element.
 21. In an electriccompressed-gas circuit breaker as set forth in claim 8 wherein saidnozzles are radially disposed to said contact ring.
 22. In an electriccompressed-gas circuit breaker as set forth in claim 8 further includinga guiding structure on said contact ring at the free end face of saidbridging switching element and at least some of said holes terminatetherein.